A Probalistic Model for the Accumulation of Fatigue Damage in Composite Laminates

Abstract

A stochastic model for the accumulation of fatigue damage in composite laminates in terms of stiffness loss is proposed. The model considers the accumulation of fatigue damage as an evolutionary stochastic process and represents the distribution of stiffness loss in a laminate as a function of the number of load cycles. Stiffness loss is modeled as an embedded discrete time, finite state, and nonstationary stochastic process; it utilizes a discrete time, finite state, stationary Markov model in conjunction with a time transformation-condensation method. The principle damage mechanisms associated with stiffness loss are examined within the framework of the so-called critical element model. The applicability of the proposed model is demonstrated by considering the accumulation of fatigue damage in terms of changes in the dynamic longitudinal secant modulus of graphite/epoxy laminates cycled under constant amplitude, sinusoidal, tension-tension fatigue loads.